The present invention relates to vertical take-off and landing aircraft and, more particularly, to an improved vertical take-off and landing aircraft featuring a turbofan powered, compound autogyro with retractable rotor blades and vectored thrust.
World runway congestion is an acute and growing problem evoking costly delays for both air carriers and passengers. This serious situation is forecast to go critical in the early years of the next century. By the year 2016, for instance, all forecasts indicate that global enplanements will triple over 1990 levels but runways will not keep pace.
While there will be some new runways and airports built in the future, plus an improved management of air space, major markets such as New York, Chicago, Frankfurt and London will not experience a sufficient enhancement of runway capacity. Aircraft noise and other environmental concerns form the chief restrictions to airport development. But pervasive land use and high costs are also factors.
Clearly, there is an urgent need for a large, safe, vertical take-off and landing vehicle (VTOL) operating off Verti-pads at major airports. These VTOL operations, mostly on short haul service, would help free up runways for conventional jets.
The unique design of the VTOL aircraft of this invention addresses the congestion problem, and is useful as a vehicle for humanitarian and disaster relief. It can also find applicability in timbering, fire fighting, defense employment and delivering social services to remote regions of the Third World.
The new aircraft of this invention is believed to be capable of changing many aspects of the aviation industry. While the design incorporates most of the attributes of a helicopter, the aircraft operates on the autogyro principle. Independent lift and propulsion systems are incorporated in the aircraft in a manner known in the trade as a compound autogyro, sometimes referred to as a converti-plane.
Designers, since 1946, have attempted to combine the best qualities of the airplane and the helicopter, while avoiding the limitations that each aircraft presents. The xe2x80x9cROTODYNExe2x80x9d was a compound autogyro invented in England, and was successfully demonstrated on test routes in Europe. It proved that it was indeed possible to design a safe VTOL airliner capable of lifting 70 passengers.
Alongside this development, the tilt rotor VTOL became popular in the United States. The tilt rotor, however, was not the answer for civil operations, owing to the fact that it was sized improperly. It was also troubled by a series of fatal accidents. The tilt rotor VTOL was limited to about 40 passengers, far too limited to achieve a profitable seat mile rate. Additionally, the tilt rotor was propulsion restricted to the available turboprop engines, or a cruise speed of about 340 mph, too slow to meet the 21st Century air carrier demands, even on short stage length routes.
Common misconceptions with respect to vertical lift aircraft have been widely held in the industry. Despite the existence of the ROTODYNE aircraft, the air carrier industry seems to doubt that a safe, fast, comfortable, 145-seat VTOL commercial airliner can be designed. Many mistakenly believe that such aircraft cannot be designed with backups such as two and three hydraulic systems, redundant pumping, two electrical systems, etc., which are common on conventional jet transports. Another misconception with respect to VTOL aircraft has been that turbofans could not be employed, or were somehow incompatible with rotary-winged aircraft.
A workable VTOL of this invention uses proven and demonstrated technology, and is commercially practical.
The inventive VTOL has an operating envelope between hover, or zero mph, and 520 mph. It can also stop in mid air, and back up by reversing the flow of the turbofan""s exhaust.
The VTOL airliner of this invention is an assembly of proven systems designed to provide a comfort zone for air carriers and passengers alike.
The VTOL airliner of the invention operates as a conventional airliner, employing its blade system only when entering terminal air space on take-offs or landings.
The VTOL of this invention, above all else, is safe. The inventive VTOL airliner is designed with fail-safe and redundant systems, such as those featured on conventional commercial aircraft.
In the preferred embodiment of this invention, the VTOL aircraft features two independent power systems. One set of augmented turbofans, proven military engines, are employed to power the rotor blades via a reactive drive system known in the industry as the hot cycle which eliminates the need for a tail rotor and complicated reduction gearing.
Another set of engines, known in the industry as high by-pass turbofans, are employed for the cruise portion of the flight, while the augmented turbo fans are taken off line.
The inventive aircraft has a retractable rotor. Should the rotor system fail to descend into the fuselage when a retraction command is given, the rotor will simply windmill. Should the rotor system fail to pump up for a landing, then the landing can be accomplished via conventional fixed wing and rear thrust options. These options make the VTOL of this invention extremely safe and reliable. The duality of lift and propulsion, plus the available emergency downthrust, provides a safety net for a mechanical or structural failure, or when operating in areas of critical icing and xe2x80x9cdownbursts.xe2x80x9d
Another advantage of the invention is its seating design. Airliners such as the 737, 757, etc., called narrow bodies, can arrange first class or business class seating only at four abreast. The 737-300 series has a fuselage transverse section of 139 inches. In comparison, the present invention can achieve first class seating with six abreast, by adding 32 inches on the breadth of the fuselage, for a total of 171 inches. This allows the carrier to offer 96 high priced seats to business travelers. The simple design change also offers a three and four offset aisle arrangement comprising 150 coach class seats, plus a twin aisle layout for six abreast seating. An additional advantage of this aircraft is its ability to operate in a fully competitive regime as a fixed wing, conventional jet without employing the rotor mast. This design element should increase the vehicle""s service flexibility.
Typically, in a vertical lift vehicle such as a helicopter, forward speed is limited due to the onset of compressibility in the retreating region of the blade path. Realizing this constraint, designers have attempted to combine the strongest flight mechanics of the helicopter and the fixed wing aircraft.
One such design is that of the tilt rotor, whereby the engines are faced upward for take-off and then tilt downward for conventional cruise flight. However, current turboprop engines employed by the tilt rotor do not have sufficient horsepower to lift a vehicle large enough to carry a sufficient payload for commercial and humanitarian purposes.
Another scheme for combining the qualities of the helicopter and the conventional aircraft is disclosed in U.S. Pat. No. 3,986,686. This vehicle features a four-bladed rotor in the xe2x80x9cXxe2x80x9d configuration which houses two blades against the airframe, while the two other airfoils form a fixed wing. This design, however, stops the rotary wing in flight, in order to convert this airfoil into a fixed wing. This is clearly unacceptable for high load, cargo and passenger operations. Computational fluid dynamic models have indicated that during the transition from rotary wing to fixed wing flight, oscillations, vibrations and instability problems arise. Additionally, the geometry, wing loading, high lift devices of a fixed wing are inconsistent with the attributes of a rotary wing. The compromise between the two airfoils, even if the transitional problems could be solved, would result in a high drag vehicle with L/D (lift over drag) ratios around ten or less. A modern airliner operates with L/D values of about 15, which is both fuel efficient and aerodynamically sound.
In accordance with the present invention, there is provided a commercial vertical take-off and landing (VTOL) vehicle. The VTOL aircraft is a turbofan powered, compound autogyro that employs retractable, rigid rotor blades. The VTOL vehicle comprises a rotor mast that retracts into the fuselage of the aircraft. The retraction device includes a cylindrical mast that moves up and down, and an outer cylinder propelled by a series of hydraulic actuators, or scissor lifts, affixed to a bottom section of the fuselage. The upper portion of the mast is free moving in both the horizontal and vertical planes. Located in the upper mast are twin gas lines leading to a hub section of the rotor. In the hub, the gas lines divide the mass flow into two additional gas lines reaching to the tip ends of the rigid rotor blades.
A revolving, upper section of the rotor mast is attached to a lower, non-rotating section by a spherical bearing. Directly beneath this attach bearing is a distribution plenum, which receives the mass flow from each of two augmented turbofan engines. To achieve high levels of safety not known to present VTOL aircraft, the turbofans are equipped with vectoring vanes that direct the mass flow to the plenum or, in the alternative, out a jet pipe for conventional flight propulsion. Another set of vectoring vanes can direct the mass flow downward, to stabilize the inventive VTOL vehicle in case of a serious problem upon take-off, when close to the ground. In this emergency condition, all available turbofans supply mass flow to the plenum, which allows for continuous take-off climb, or a return to a controlled landing via the downward deflection of the vectoring vanes.
Cascade jets are positioned at the tip end of the rotor blades to supply additional velocity levels to the mass flow. Also, at the tip end section of the rotor blades are hydraulically operated, pop-up vanes that center the rotor wing fore and aft in the slip stream. Once positioned, the rotor is then retracted to form the upper skin of the fuselage.
These features provide both redundant and fail-safe characteristics for the inventive VTOL aircraft which are not provided on similar air vehicles. The variable geometry and vectored thrust allow vertical take-offs and landings while permitting cruise speeds of Mach 0.82. The VTOL aircraft can lift a payload of about 34,000 pounds, which is equivalent to carrying around 145 passengers. The inventive VTOL has a sustained lift that is divided into two independent systems:
1. For take-offs, the VTOL vehicle employs a multi-bladed rotary airfoil, propelled by two augmented turbofans via a reactive drive system known as a hot cycle. Lift is transferred to a fixed wing after the aircraft has established a positive climb rate. During this flight phase, the rotary wing is positioned fore and aft via a pop-up vane, which centers the airfoil in the slipstream. The variable geometry xe2x80x9cVxe2x80x9d tail is then revolved from a downward position where it does not conflict with the rotor path to an upward position for cruise flight.
2. Once aligned, the rotary wing is retracted into a well, so that the airfoil forms, and becomes the top section of the fuselage, as aforementioned. For redundancy, each of the four turbofans of the VTOL employs three modes of operation:
a. For take-offs and landings, all exhaust gases are directed into the distribution plenum at the base of the retractable rotor mast, then upward to the rotor tips.
b. Each engine can direct the exhaust gases rearward for forward cruise flight.
c. In a low altitude emergency, the thrust from the four engines may be directed downward, via vectoring vanes, to cushion a hard landing.
It is an object of this invention to provide a commercial VTOL aircraft.
It is another object of the invention to provide an improved VTOL aircraft that has built-in system redundancy for safety purposes.